Hematocrit measuring method

ABSTRACT

A method for measuring a hematocrit ratio for a sample of blood comprises the steps of passing electromagnetic energy through the blood sample, measuring a characteristic representative of the amount of energy absorbed by the sample, and computing the hematocrit ratio by applying a proportionality factor to the measured characteristic of absorbed energy.

United States Patent [191 Shuck 1 Dec.2,1975

[ 1 HEMATOCRIT MEASURING METHOD Reginald C. Shuck, Orlando, Fla.

[73] Assignee: Stephen E. Dolive, Orlando, Fla. a

part interest [22] Filed: May 29, 1974 [21] Appl. No.: 474,170

[75] Inventor:

3,740,143 6/1973 Groner et al. 1. 356/39 3,817,632 6/1974 Picunko et11].. 356/39 3,830,569 8/1974 Meric 356/39 Primary ExaminerR. V. RolinecAssistant Examiner-Darwin R. Hostetter Attorney, Agent, orFirm-Duckworth, Hobby & Allen [5 7] ABSTRACT A method for measuring ahematocrit ratio for a sample of blood comprises the steps of passingelectromagnetic energy through the blood sample, measuring acharacteristic representative of the amount of energy absorbed by thesample, and computing the hematocrit ratio by applying a proportionalityfactor to the measured characteristic of absorbed energy.

12 Claims, 4 Drawing Figures LIGHT I a 30 l0 [7 COLL/MA TOR CUVTTE 501/r 1 PH 1 13b 26 2.. 0 OCELL 38 I6 22 24 2o 32 APERTURE EL 50 mo/wc cmcu/rs FIG. 34 REFERENCE GALVANOME TER PHOTOCELL 3s DECODER Aaco '5 DATA05c,

US. Patent Dec. 2, 1975 Sheet 2 m2 3,923,397

DE C 005 R5 PR/N TER CONTROL c/ cu/ r PR/N TEE AMPLIFIER A our/ ur (a)CLOCK/C CLOCK (c) E 005 7 0 l 2 3 4 5 6 7 0 SWITCH $50. 3 3 2 3 d) FIG.4

HEMATOCRIT MEASURING METHOD BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates to systems and methods fordetermining the volumetric ratio of liquid suspended solids with respectto the suspending liquid. In

particular, the present invention relates to systems and methods formeasuring hematocrit, which is the percent ratio of blood cells per unitof whole blood.

2. Description of the Prior Art Hematocrit is defined as packed bloodcell volume, generally expressed as a percent per 100 milliliters ofwhole blood.

Hematocrit is one of several laboratory determinations with respect tored blood cells in human blood, or the blood of other animals. Two otherallied determinations are that of red blood cell count per cubicmilliliter and hemoglobin, which is expressed as grams per 100milliliters. To a hematologist, computations of ratios involving thesethree determinations are of considerable value.

The first of these ratios is the mean corpuscular volume (MCV) which isdetermined by multiplying hematocrit by 10 and dividing the result bythe red blood cell count expressed in millions per cubic millimeter,such that MCV is expressed in cubic microns. This ratio approximates redblood cell (erythrocyte) size.

The second ratio is the mean corpuscular hemoglobin (MCH) which isdetermined by multiplying hemoglobin by 10 and dividing the result byred blood cell .count expressed in millions per cubic millimeters, suchthat MCH measurements are expressed in micromicrograms. This ratioapproximates the hemoglobin per cell by weight.

The third ratio is the mean corpuscular hemoglobin concentration (MCHC),which is determined by multiplying hemoglobin by 100 and dividing theresult by the hematocrit. This ratio is expressed in percent, andapproximates hemoglobin concentration in red blood cells by volume. Ofthese three ratios (MCV, MCH, and MCHC), only MCH may be calculatedwithout knowledge of the hematocrit.

Hematocrit has traditionally been determined in the laboratory bycentrifuging small tubes of blood in order to pack the cells in thebottom of the tubes. Results obtained in this manner, which is referredto as microhematocrit, vary as between centrifuges and operators.

Automated equipment for measuring hematocrit fall into two categories.One such arrangement employs the centrifuging techniques discussedpreviously, with automatic loading, unloading and interpretation.

The second type of automated hematocrit measuring system involveselectronic processing of signals obtained by measuring conductivity inproportion to cell size when a dilute solution of cells is passedbetween two electrodes. Examples of this type of arrangement aredescribed in U.S. Pat. No. 3,692,410 to Jurany et a]. and U.S. Pat. No.3,439,267 to Coulter et al.

In addition, other types of automated blood analyzing systems arecommercially available which are not capable of determining hematocrit.Many of these systems utilize photometry techniques, whereby acharacteristic of the amount of light absorbed by a blood sample isprocessed to determine red blood cell count and hemoglobin.

Other systems and techniques for analyzing the volumetric or particulateratio of liquid suspended particles are disclosed in the following U.S.Pat. Nos. 3,740,143 to Groner et al.; 3,646,352 to B0] et al.; 2,775,159and 3,045,123 to Frommer. Carr, in U.S. Pat. No. 3,714,444, discloses areflective light measuring system employing a logarithmic ratioconverter for providing a single output representative of theconcentration of suspended solids.

With respect to the measurement of MCV, Stevens, in U.S. Pat. No.3,084,591, discloses a system for measuring this characteristic.Pelavin, in U.S. Pat. No. 3,634,868 teaches an automatic calibrationcircuit useful in fluid sampling systems.

SUMMARY OF THE INVENTION The present invention contemplates a method formeasuring a hematocrit ratio for a blood sample, comprising the steps ofpassing electromagnetic energy through the blood sample, measuring acharacteristic representative of the amount of the energy absorbed bythe sample, and computing the hematocrit ratio by applying aproportionality factor to the measured characteristic of absorbedenergy.

An essential aspect of the present invention is the recognition that thehematocrit ratio is directly proportional to the amount of lightabsorbed by blood cells in any given quantity of diluted blood. Anelectronic system for automatically computing hematocrit in accordancewith the method of this invention is disclosed in a U.S. patentapplication entitled SYSTEM FOR MEA- SURING VOLUMETRIC RATIOS OF LIQUIDSUS- PENDED SOLIDS, filed by Stephen Dolive on an even date with thisapplication.

DRAWINGS FIG. 1 is a block diagram illustrating an arrangement ofapparatus employed with the present invention.

FIG. 2 is a schematic circuit diagram of a portion of the apparatusshown in FIG. 1.

FIG. 3 is another schematic circuit diagram of a portion of theapparatus of FIG. 1.

FIGS. 4(a), (b), (c) and (d) are diagrams illustrating voltages andswitching sequences of the circuits shown in FIGS. 2 and 3.

DETAILED DESCRIPTION A. Method A method for determining hematocrit ratioof whole blood will now be described with reference to the apparatusshown in FIG. 1.

The apparatus of FIG. 1 includes a photometer, referred to generally as10, having a monochromatic light source 12 for producing a light beam 13along the beam path. The photometer 10 may also include a beamcollimator 16 if required. It will be understood by those skilled in theart that various other light source arrangements may also be employed..For example, a non-monochromatic light source may be employed incombination with filtering means to produce a monochromatic output.Suitably, the light in the beam 13 is of a color which is complementaryto the color of blood. For example, a green or blue color source isbelieved suitable.

The photometer 10 may further include a beam splitter 18 for directingone-half of the energy in the beam (identified at 13b) normal to theremainder of the beam 13a. A suitable enclosure 20 is provided forholding a blood sample container (cuvette) 22, which contains a dilutedblood sample 24 the hematocrit ratio of which is to be measured.Preferably, the blood 24 is diluted with a physiological saline solutionto a consistency suitable for determining hematocrit. This salinesolution may comprise sodium chloride having a concentration on theorder of 0.85%.

The enclosure 20 further includes suitable apertures 26, 28 aligned withthe source 12 so as to allow the beam portion 130 to pass through thecuvette 22, the diluted blood sample 24 and thereafter impinge upon aphotocell 30, which detects the amount of light in the beam portion 13atransmitted through the blood sample. Again, it will be understood bythose familiar with the optics art that a wide variety of opticaltechniques may be used to provide a light beam through the euvette 22which is balanced with respect to a reference portion of the beam, aswith the one embodiment described next.

The split portion 13b of the beam 13 is suitably directed through anadjustable aperture 32 and then impinges on a reference photocell 34,which detects the amount of light energy in the split beam portion 13b.Signals representative of the light detected by each photo cell 30, 34is then fed into a galvanometer 36, which compares the signal levelsfrom the two photo cells and displays, usually with a deflecting needlemeter 37, the percent of light transmitted through the blood sample 24with respect to the light energy in the split beam portion 13b.Alternatively, the meter 37 may be calibrated in absorbance, which is ameasurement of the amount of light absorbed by the blood cells in thesample 24 with respect to the amount of light which would be passedthrough the cuvette 22 without the presence of the blood sample (asrepresented by the energy in split beam portion 13b). The relationshipbetween absorbance and transmission is given by the expression:

(1) Abs. =2 log T where:

Abs. Absorbance;

T per cent of light passing through sample with respect to the incidentlight.

The photometer described thus far is essentially similar to a class ofcommercially available photometers generally referred to ascolorimeters, which have been widely employed in the measurement ofhemoglobin. Another class of photometers, referred to asspectrophotometers, may likewise be employed with this method.Spectrophotometers are more complex than colorimeters, and usuallyinclude a diffraction grating through which the light beam is passed toproduce a spectrum. The output of the diffraction grating is thenmechanically and optically manipulated, resulting in a beam of light ata carefully calibrated wavelength and band width.

Again noting FIG. 1, the outputs of the photocells 30, 34 may betransmitted to an electronic circuit 38, an embodiment of which isdescribed below under Section In accordance with the method incorporatedin the present invention, the hematocrit ratio of the blood sample 24 isdetermined as directly related to either the transmission or absorbancecharacteristic of the light passing therethrough. The hematocrit ratiois expressed with respect to absorbance as follows:

(2) HCT K(Abs.)

where:

spect to the transmission characteristic as follows:

(3) HCT K(2 log T) In accordance with the present invention, theproportionality factor K in expressions 2 and 3 above is given by:

HCT,

Abs,-

where:

K proportionality factor;

HCT hematocrit ratio of a standard blood sample measured by any knowntechnique;

Abs. the amount of light absorbed by the standard blood sample.

Thus, in order to determine the proportionality factor K, the hematocritratio of a standard blood sample S is measured by any known technique.Preferably, this is done by the centrifuging (micro hematocrit)technique described above with respect to the prior art. The standardblood sample S is then diluted with a physiological saline solution andplaced in the photometer l0 and the absorbance (or transmission)characteristics of that sample S is measured in the manner describedabove. While the absorbance characteristic of the sample S may bedetermined on another photometer, it is preferable to employ the samephotometer 10 which is used to measure the absorbance of the sample 24,in order to offset any inherent errors between two differentphotometers.

By employing expressions 2 and 4 above, the unknown hematocrit of thesample 24 is given as:

HCT Abs,

It will be understood that the hematocrit and absorbance of the standardblood sample S need not be measured each time an unknown hemaotcrit isto be determined. Suitably, the meter 37 of the galvanometer 36 isprovided with calibration means which allows a variable K to beincorporated in the meter reading, and then the K is adjusted byoccasionally measuring a standard sample: for example, once a day, orwhenever a new batch of saline solution is to be used, since theproportionality factor K may vary dependent on differences in suchsaline solutions. Further, the proportionality factor may vary betweenphotometers, and it therefore is desirable to employ the same photometerfor measuring both samples. The electronic circuits 38 may provide meansfor automatically computing the unknown hematocrit of the sample 24under test, to provide an automatic printout for visual disply of thehematocrit ratio, as is described next.

B. Electronic System An electronic system useful for measuring thehematocrit ratio of whole blood, as well as volumetric ratios of otherliquid-suspended solids, is shown and described with reference to FIGS.2, 3 and 4, in which HO. 2 illustrates an embodiment of an amplifier,charge storage and logarithmic conversion circuit. while FIG. 3illustrates digital circuitry useful with the embodiment of FIG. 2, inwhich inputs to and outputs from FIG. 2 with respect to FIG. 3 havecommon designations.

The circuit in FIG. 2 includes capacitors and resistors, as well asintegrated amplifiers, electronic switches and digital circuitry all ofwhich are illustrated using symbols well known to those skilled in theelectronic art. Each component is identified in FIG. 2 with anappropriate upper case letter, such as capacitor C, resistor R,amplifier A, switches S, and so forth, followed by a lower casereference numeral or letter. While specific values and examples of thecircuit components are set forth in the attached Appendix, it will beunderstood that changes in the circuit values or in the selection ofcomponents can be made without departing from the scope of the presentinvention. (1) Photocell detection and logarithmic conversion.

The photocell detection and the logarithmic conversion circuit, referredto generally as 50, is shown in FIG. 2. The circuit 50 includes twoelectronic switches S, and S which are respectively coupled to thereference photocells 34 and the cuvette photocell 30 (note FIG. 1). Theoutputs of switches S, and S are both coupled to the inverting input ofan operational amplifier A, through a gain determining resistor R,, andto ground through another switch S The output of amplifier A, is coupledto the inverting input of another operational amplifier A throughresistor R The output of amplifier A is coupled back into thenon-inverting input of A, through resistors R R and R through switch Sto the non-inverting inputs of amplifiers A through resistors R andswitch S and to the noninverting input of amplifier A,,, throughresistor R and switch S The outputs of amplifiers A and A are coupled tothe inverting and non-inverting inputs, respectively, of comparatoramplifier circuit A Amplifiers A and A, are connected as voltagefollowers, with the output also fed back into the inverting inputthereof.

Reference is again made to amplifiers A, and A Capacitor C,, serving asa stabilizing capacitor, is coupled between the junction of resistors Rand R and to ground. Resistors R and R are feedback resistors coupledbetween the respective outputs of amplifiers A, and A to the invertinginput thereof. Resistor R is coupled between the noninverting input ofamplifier A and ground.

Referring to the right hand portion of FIG. 2, a capacitor C is coupledbetween the output of switch S and ground, and another capacitor C iscoupled between the output of switch S and ground. A potentiometer R,having a wiper terminal shorted to one side, is coupled across capacitorC,,,, to switch S and resistor R to ground. Resistor R, is coupledbetween the output of switch S to the wiper of a potentiometer R,,,,which serves as a dropping resistor between the positive and negativeterminals of a voltage source.

Each of the switches S, S inclusive, are controlled by respective NANDgates 52, 53, 54 and 55. Switches 5 and S are controlled by inverters 56and 57, and switch S is controlled from the L output of the digitalmultiplexing circuit, described below. The NAND gates and inverters52-57, inclusive, are coupled to the 07 outputs of a one-out-of tendecoder circuit-58, which is driven by a BCD decade circuit 60. It willbe appreciated that the circuits 52-58 are equivalent in fuction todevices such as programmable read only memories (PROM).

2. Digital Control Circuit FIG. 3 illustrates a digital circuit,referred to generally as 70, for controlling the circuit 50, of FIG. 2.The circuit includes an inverter Schmitt trigger 72, the input of whichis coupled to the output C of the comparator A of FIG. 2. The circuit 70further includes two single pole double throw switches 74 and 75, orequivalent means, to initiate operation of the circuits 50 and 70, asdescribed below.

As shown in FIG. 3, there is also included three data registers 71, 73and 77, two of which registers 71 and 77 are respectively identified asthe least significant digit LSD register and the most significant digitMSD register. All three registers 71, 73 and 77 are coupled to decodercircuit 79, which in turn feeds a printer control circuit 76,controlling a printer 78.

The circuit 70 additionally includes a plurality of digital NAND andinverter gates, as well as associated resistors R R and capacitors C andC Each of these components are depicted by commonly accepted symbo ls inthe drawing. As shown in FIG. 3, these components are coupled to provideoutputs thereof as represented by the following symbols:

C Output of comparator A G Output from Schmitt. trigger 72.

G Gate output indicating that N/O contacts of switch are closed.

G Gate output indicating that N/O contacts of switch 74 are closed.

G Gate output that is high when the switch multiplexer decoder 58 is inthe zero position.

G Gate output to data register 71 input.

G =Logarithmic conversion activation gate.

C Output from clock oscillator.

C Output gate that generates momentary high pulse when C changes statefrom low to high.

G Latch set gate.

L Error preventionlatch.

L Multiplexer control latch L Data control latch L Printer controllatch.

The circuit 70 of FIGS. 3 serves to provide clocking and controlfunctions to the circuit 50 of FIG. 2, and it will be recognized bythose skilled in the electronic arts that various modifications may bemade to the circuit 70 to accomplish this purpose.

3. Operation of System One cycle of the operation of a system embodyingcircuits 50 and 70 will now be described.

Initially, the cuvette 22 containing the blood sample 24 under test isplaced in the container 20. The switch 74 is then activated, connectingthe normally open terminal NIC to ground. This may be done manually, oralternatively, a microswitch or equivalent means may be placed with thecontainer 20 to detect the presence of the cuvette 22. When switch 74 isclosed, latch L,,, is set by NAND gatmmchanges to its low state and setsL which activates the amplifier system 50. Simultaneously, L is resetand L,, is held in its reset condition. The resetting of L partiallypreconditions G Thereafter, comparator output C and gate output G arestabilized in their high states, further preconditioning G and partiallypreconditioningi: G is low and prevents the setting of L by the pulsingoutput of C The reset inputs to all three data register decades are heldhigh by G thereby entering and maintaining zero in all three decades.

Referring for a moment to FIGS. 2 and 4, the decoder 58 provides a clockoutput like that shown in FIG. 4b, the corresponding output designation-7 inclusive, being shown at FIG. 4c. At the beginning of clock output7, only switch S is turned on. This provides a ground reference signalto the amplifier combination of A, and A During the next clock period 0,switch S remains on and switch S is turned on. The turning on of switchS, causes the error output voltage of amplifier A to be stored oncapacitor C,. In accordance with the present invention, the storing ofthat output results in the correction of the inherent offset error ofthe amplifier circuit A, and A by briefly closing switch S, to chargecapacitor C,, thereby momentarily reducing the gain of the amplifiercircuit to approximately I. When the amplifier circuit of A, and A issubsequently called upon to amplify a signal, that amplifier isreferenced to true ground.

During clock period 1, only switch S, is closed, causing the output ofthe reference photocells 34 to be fed into amplifier circuit A, and AThe opening of switch 8., allows the amplifier circuit A, and A toamplify that reference photocell signal (not waveform 100 in FIG. 4a) byan amplification factor determined by its design characteristics. Thisamplification continues as long as switch S, is closed; that is, duringclock periods 1 and 2. At the beginning of clock period 2, switch S isclosed, causing the capacitor C to start charging on the output ofamplifier A through resistor R Assuming normal clock rates, on the orderof 0.3 1O Kilohertz, capacitor C does not charge completely until switchS has cycled closed several times. However, the charging of capacitor Cis completed within the 3-3 second period described below, withreference to the operation of switch 74 in FIG. 3.

Clock periods 3 and 4 repeat clock periods 7 and 0, conditioning theamplifier circuit A, and A as described above. During clock periods 5and 6, switches S and S are sequentially turned on, allowing the outputof the cuvette photocell 30 to be amplified and stored in capacitor C inthe same manner as described above with reference to the output of thereference photocell 34 and capacitor C,.,.; (note amplified cuvettephotocell waveform 102 in FIG. 4a).- After a number of these cyclesoccur, both of the capacitors C and C are charged to a levelrepresentative of the outputs of the respective photocells 34 and 30.

Refer again to FIG. 3. A period of time after L is set, on the order of3 seconds, the switch 74 is moved to the normally closed pole N/C, whichreturns G to its low state. GJbecomes high, preconditioning I; When theoutput of the decoder 58 is zero, G goes high, further preconditioning GWhen C, momentarily goes high with the falling edge of the clock pulse,G goes low setting L,,, which turns on switch S and resets L This 3 15second time delay is provided to allow turbidity conditions in the bloodsample to stabilize and to allow the charging of capacitors C and C, toalso stabilize, as described above. It will be understood that theswitching functions of switch 74, and switch 75 described below, may bemade responsive to the mechanical position of the probe, or similarmeans, which may be used to inject the blood sample and a salinesolution into the cuvette 22. A hemoglobin and red blood cell countmachine manufactured by Fisher Scientific Instruments, Inc., ofPittsburgh, Pa., referred to as the Model 400 Hemalyzer, employ amechanical probe of this type.

Refer again to FIG. 2. The turning on of switch S, connects R to avoltage provided across potentiometer R,,,, which is divided throughresistors R and R This causes the charge stored on capacitor C todecrease logarithmically toward the junction of resistors R and R Whenthe. charge on capacitor C,,., is drained to a level equal to the chargestored in capacitor C the output of C of comparator A goes low, whichsnaps the NAND Schmitt trigger 72, resetting G and L and setting L Thisturns off switch S (note output L in FIG. 3). At this point, it shouldbe noted that the network formed by resistors R, and R, andpotentiometer R provides means for adjusting the ground reference ofresistor R thereby allowing the discharge rates of capacitors C and C tobe altered in the event that a constant output error from amplifier A 2is present.

During the period when switch S is closed, oscillator pulses enter theregister L through gate G from C When switch S, is open, this oscillatorpulse train is terminated and the number of pulses representative of thetime required to discharge capacitor C to the level of capacitor C isstored in the three registers 71, 73 and 77. It will be understood thatresistor R,,, (FIG. 2) provides a means for adjusting the period ofclosure of switch 8,, much in the same manner as the proportionalityadjustment would be made to the galvanometer 36 in FIG. 1.

Switch 75 of FIG. 3 is then closed grounding the normally open contactNO; as noted previously, this may be accomplished manually, orautomatically by detecting the lifting of a probe or the cuvette 22(FIG. 1). Upon the closing of switch 75, G goes high, preconditioningthe capacitor-resistor network of R R and C Switch 75 is returned to thenormally closed N/C position, causing L to set, activating the printercontrol circuit 76, and printer 78. The hematocrit ratio is then readout of the three data registers 71, 73 and 77 via the decoders 79.

As noted above, an essential aspect of the present invention is therecognition that the hematocrit ratio of a diluted blood sample isdirectly proportional to the amount of light absorbed by the dilutedsample. Stated conversely, the hematocrit ratio is inverselyproportional to the amount of light transmitted through the dilutedsample as is set forth above in equation 3.

The method of determining hematocrit set forth above lends itself toelectronic processing techniques as incorporated in the systemdescribed. It will be appreciated by those skilled in the medicalelectronics art that this system may be readily integrated withcommercially available systems capable of measuring the blood indices,excepting hematocrit.

Since hematocrit is used by physicians as a diagnostic tool, it isessential that the electronically measured hematocrit be free fromoffset voltage errors. In the system described above, this isaccomplished through the use of a reference capacitor and associatedswitching means to detect the offset voltage error as an output from theamplifier, and thereafter correct subsequent amplified output by theamount of the offset error.

It willbe understood by those skilled in the art that the logarithmicdetermination of transmission for purposesof expression (l above isinverted in the circuit 50 of FIG. 2, thus arriving at the result of Zlog, T, Z being the logarithm of I00.

APPENDIX Element Value R 8.2 Kohm R l Kohm R;, I Kohm R 47 Kohm R l MohmR. 4.7 Kohm R, 4.7 Kohm R 100 Kohm R I Kohm R selected according toclock frequency and C 12 selected according to R amplifier groundreferenced output u R l0 Kohm R Kohm R 10 Kohm R 2.2 Kohm R 10 Kohm R 10Kohm R l Kohm R l Kohm C, 0.l microfarad Cm l uf to 5 pl dependent onclock frequency our See C"! C 0.0l microfarad C 0.001 microfarad RCACDI6 AE S, 8, A National Semiconductor LM-308 A; National SemiconductorCorporation LM-74I A; National Semiconductor Corporation LM-3Il TexasInstruments 7490 v Texas Instruments 7442 Texas Instruments 7490 71, 73and 77 58 II II ll I claim: 1. A method for measuring a hematocrit ratiofor a diluted blood sample, comprising the steps of:

the step of centrifuging said known sample to determine said hematocritratio thereof.

3. The method recited in claim 1 wherein said characteristic of saidknown sample is determined by:

passing electromagnetic energy through said known sample; and

measuring a characteristic representative of the amount of energyabsorbed by said known sample.

4. The method recited in claim 1 further comprising the step of dilutingsaid blood sample with a saline solution prior to passing saidelectromagnetic energy therethrough.

5. The method recited in claim 4 wherein said saline solution comprisesa physiological saline solution.

6. The method recited in claim 1 wherein said electromagnetic energycomprises a beam of light.

7. The method recited in claim 6 wherein said absorbance characteristicmeasuring step comprises comparing an unobstructed beam of said lightwith said beam passing through said blood sample.

8. A method for measuring a hematocrit ratio for a blood sample,comprising the steps of:

diluting said sample;

passing a beam of light through said sample;

measuring a characteristic representative of the amount of lightabsorbed by said sample;

measuring the hematocrit ratio of a standard sample by a knowntechnique;

passing a beam of light through said standard sample;

measuring a characteristic representative of the amount of energyabsorbed by said standard sample; and

calculating the hematocrit ratio of said sample by dividing saidstandard sample hematocrit ratio by the absorbance characteristicthereof and multiplying the resulting ratio by the absorbentcharacteristic measured for said sample.

9. A method for measuring a hematocrit ratio for a blood sample,comprising the steps of:

passing a beam of light energy through said sample;

measuring the amount of said light energy transmitted through saidsample; and

computing said hematocrit ratio by applying a proportionality factor tosaid. measurement of transmitted light energy by the followingexpression:

H K (2 log T) where:

H hematocrit sought to be measured;

T measured transmitted light energy; and

K said proportionality factor.

10. The method recited in claim 9 further comprising the step ofdiluting said blood sample prior to said beam passing step.

11. The method recited in claim 10 wherein said diluting step comprisesadding an amount of a physiological saline solution to said bloodsample.

12. The method recited in claim 11 werhein said proportionality factoris determined by:

passing a beam of light energy through a known blood sample diluted withsaid saline solution;

measuring the amount of said light energy transmitted through said knownsample; and

measuring the hematocrit of said known sample by a known technique; and

computing said proportionality factor by employing said hematocrit andtransmission measurements in that expression set forth in claim 10 aboveand solving said expression for said proportionality fac- IOI'.

1. A method for measuring a hematocrit ratio for a diluted blood sample, comprising the steps of: passing electromagnetic energy through said blood sample; measuring a characteristic representative of the amount of said energy absorbed by said sample; determining a proportionality factor by dividing the hematocrit of a known blood sample by said characteristic of said known sample; and computing said hematocrit ratio by applying said proportionality factor to said measured characteristic of absorbed energy.
 2. The method recited in claim 1 further comprising the step of centrifuging said known sample to determine said hematocrit ratio thereof.
 3. The method recited in claim 1 wherein said characteristic of said known sample is determined by: passing electromagnetic energy through said known sample; and measuring a characteristic representative of the amount of energy absorbed by said known sample.
 4. The method recited in claim 1 further comprising the step Of diluting said blood sample with a saline solution prior to passing said electromagnetic energy therethrough.
 5. The method recited in claim 4 wherein said saline solution comprises a physiological saline solution.
 6. The method recited in claim 1 wherein said electromagnetic energy comprises a beam of light.
 7. The method recited in claim 6 wherein said absorbance characteristic measuring step comprises comparing an unobstructed beam of said light with said beam passing through said blood sample.
 8. A method for measuring a hematocrit ratio for a blood sample, comprising the steps of: diluting said sample; passing a beam of light through said sample; measuring a characteristic representative of the amount of light absorbed by said sample; measuring the hematocrit ratio of a standard sample by a known technique; passing a beam of light through said standard sample; measuring a characteristic representative of the amount of energy absorbed by said standard sample; and calculating the hematocrit ratio of said sample by dividing said standard sample hematocrit ratio by the absorbance characteristic thereof and multiplying the resulting ratio by the absorbent characteristic measured for said sample.
 9. A method for measuring a hematocrit ratio for a blood sample, comprising the steps of: passing a beam of light energy through said sample; measuring the amount of said light energy transmitted through said sample; and computing said hematocrit ratio by applying a proportionality factor to said measurement of transmitted light energy by the following expression: H K (2 - log10 T) where: H hematocrit sought to be measured; T measured transmitted light energy; and K said proportionality factor.
 10. The method recited in claim 9 further comprising the step of diluting said blood sample prior to said beam passing step.
 11. The method recited in claim 10 wherein said diluting step comprises adding an amount of a physiological saline solution to said blood sample.
 12. The method recited in claim 11 werhein said proportionality factor is determined by: passing a beam of light energy through a known blood sample diluted with said saline solution; measuring the amount of said light energy transmitted through said known sample; and measuring the hematocrit of said known sample by a known technique; and computing said proportionality factor by employing said hematocrit and transmission measurements in that expression set forth in claim 10 above and solving said expression for said proportionality factor. 